DESCRIPTION: The long term goals of these experiments is to apply cellular and molecular control mechanisms to guide the reconstruction of complex neocortical circuitry by neural transplantation of genetically modified precursor cell lines, making possible new avenues of treatment for developmental, metabolic, degenerative or acquired neocortical diseases responsible for mental retardation and other sensorimotor and cognitive dysfunction. In neocortex, the effectiveness of potential transplantation therapy may depend critically on whether donor cells can migrate to correct locations, differentiate and integrate appropriately and reestablish the precise long distance projections that form the basis of sensory, motor and cognitive function. Embryonic neurons and multipotent neural precursors transplanted into regions of neocortex undergoing photolytically- induced apoptotic neuronal degeneration of pyramidal neurons can respond to reexpressed developmental signal molecules, selectively migrate into these regions, differentiate into pyramidal neurons, accept afferent synaptic input, and reform distant projections with specificity. The signal molecules include specific upregulation of the neurotrophins BDNF, NT-4/5, and Nt-3. Selective neuronal apoptosis is induced by long wavelength laser energy that penetrates through nervous system tissue without injury to intermixed neurons, glia, axons, vascular and connective tissue, resulting in degeneration to targeted subpopulations of neurons in vivo. Most CNS injury models are not sufficiently specific to equivalently address these cellular development and transplantation issues. Analysis is performed by anatomic, cell biological, electron microscopic and molecular methods. Specific Aim I will compare the migration, differentiation and integration of E17 neocortical neurons transplanted during ongoing apoptotic neuronal degeneration with that of neurons transplanted during chronic neuronal deficiency. Specific Aim II will investigate whether the number and specificity of donor projection neurons are affected by using defined subsets of precursors. Specific Aims III and IV will develop, characterize and apply highly specific neocortical neuronal cell lines generated with novel strategies to isolate restricted precursors to reconstruct damaged circuits, using the transgenic mouse H-2Kb-tsA58 carrying an inducible, temperature- sensitive large T antigen transgene. Specific Aim V will assess functional integration of transplanted embryonic neurons and neuronal cell lines from Aim IV, using vibrissal stimulation and analysis of c-fos induction and downstream CREB phosphorylation. The broad hypotheses under investigation are that: 1) reconstruction of complex neocortical circuitry is possible, if appropriate donor cells are guided through the correct developmental pathways by specific control signals, and 2) restricted potential primary or clonal precursors may provide more effective and efficient repopulation and formation of projections than less mature, multipotent CNS precursors or stem cells.